When you're putting together a so-called "Car PC", by which we usually mean a contemporary ATX-derivative computer installed into an automobile, you have a few hurdles to cross. The enclosure, interface, storage devices, and even the power management all become special problems. The power problems can largely be solved through the use of a Wide Input picoPSU, but what about systems outside of a 120W envelope, or systems where you need to switch more than the PC power? The answer is just one typical automotive relay.
While my experience to date with Ubuntu 10.04 has been mixed, I have found one compelling reason to employ it, at least for owners of laptops based around AMD's Athlon L110 and RS690 chipset, like my Gateway LT3201u: it has working power management support. This processor does not support typical power-saving methods, i.e. manual frequency scaling; instead, it provides support for AMD PowerNow! in the form of multiple idle states.
Once upon a time it was fashionable to use windmills for pumping water. On flat ground, an elevated water storage tank was constructed; on terrain which included hills, houses could be situated below tanks, and tanks on high ground. When the wind blew too hard, the tail cocked sideways and caused wind to blow past the blades rather than through them as a governor.